FK506 is a candidate drug for acute stroke. For such drugs, any decision to proceed to clinical trial should be based on a full and unbiased assessment of the animal data, and consideration should be given to the limitations of those data. Such an assessment should include not only the efficacy of a drug but also the in vivo characteristics and limits to that efficacy. Here we use systematic review and meta-analysis to assess the evidence for a protective effect of FK506 in animal models of stroke. In all, 29 studies were identified describing procedures involving 1759 animals. The point estimate for the effect of FK506 was a 31.3% (95% confidence interval 27.2% to 35.4%) improvement in outcome. Efficacy was higher with ketamine anaesthesia and temporary ischaemia and was lower in rats, in animals with comorbidities, and where outcome was measured as infarct size alone. Reported study quality was modest by clinical trial standards, and efficacy was lower in high-quality studies. These findings show a substantial efficacy for FK506 in experimental stroke, but raise concerns that our estimate of effect size might be too high because of factors such as study quality and possible publication bias.